Recently, as portable type electronic equipment has become smaller and has had a higher performance, a semiconductor device, etc. has been required to have a small size and high performance. In order to meet these requirements, it is necessary to increase the number of terminal pins, to reduce the pitch or to make an area arrangement. In this case, however, there is a limit for reducing the pitch. In order to further reduce the pitch, it is important to mount a terminal electrode on an element or wiring as well.
According to such a mounting, when a bump is formed or mounted on the terminal electrode provided at the semiconductor side, if extremely high pressure is applied, the element inside the semiconductor device may be destroyed or cracks may occur in an insulating layer. Thus, an electric current leak occurs between the insulating layer and the wiring. For example, in a technique using a wire boding method, the impact load may damage the element or the wiring. Therefore, a technique where a terminal electrode is provided on the element or the wiring as well has not been established. Therefore, when the wire bonding method is used, it is necessary to form a terminal electrode outside the element or the wiring. Moreover, the wiring had to be drawn out of the semiconductor device.
Therefore, in the prior art in which the area bonding can be performed, the mounting technique is mainly based on a plating bump. Examples of such techniques include a mounting technique using a solder bump. The technique is developed by IBM Ltd. and generally called C4 (Controlled Collapse Chip Connection).
FIG. 8 is a schematic cross-sectional view of a bonding structure of a semiconductor device of the above-mentioned mounting technique. An SiO.sub.2 film 116 is formed on a substrate 118 and an Al terminal electrode 117 is formed on the SiO.sub.2 film 116. On the terminal electrode 117, a solder bump 111 is formed via a glass protective film 115 and metal films 112, 113 and 114.
According to a literature "Mounting Technique of Electronics" (August (1996), pages 78-83), an aluminum oxide film is formed on the surface of aluminum that is a material of the terminal electrode 117 of an IC chip.
After removing this oxide film, the metal films, called barrier metals, 112, 113 and 114 are formed by vacuum evaporation, and then the solder bump 111 is formed. As a material for each film, for example, a Cu--Sn intermetallic compound for the metal film 112, a Cr--Cu alloy for the metal film 113 and Cr for the metal film 114 are used, respectively.
This solder bump 111 is brought into contact with an input/output terminal electrode of a circuit board and then reflow is performed. As a result, the solder bump 111 is melted and the bonding between the solder bump 111 and the input-output terminal of the circuit board is completed.
Moreover, the bump is not limited to the solder bump alone. An Au plating bump may be formed after the barrier metal is formed.
In these techniques, it is not necessary to apply load when the bump is formed. Therefore, in a case where the terminal electrode is formed on an active element of the IC chip, even if the bump is formed on the terminal electrode, the active element of the IC chip can be prevented from being damaged.
However, in these techniques, plating or treatments accompanying the plating are carried out. Therefore, a device for plating, a waste liquid treatment and a washing treatment, etc. are required, thus raising the manufacturing cost. In addition, it is necessary to cope with environmental problems, separately. Consequently, it has been difficult to put these techniques of the prior art into practical use as a consumer product.
As mentioned above, circuits of the semiconductor device have become finer. There was a problem in terms of securing an electrode for electric current to flow in such finer circuits. Furthermore, in a case where the electroless plating is performed, it is very difficult to unify the height of the bump, so that the reliability of the mounted body remains a problem.